1. Field of the Invention
The present invention relates to an air conditioner, and more particularly, the present invention relates to a method for controlling a plurality of compressors in an air conditioner to which a multi-compressor is applied in a manner such that a plurality of compressors are adopted as a compressing means for compressing refrigerant to allow an air conditioner to operate efficiently.
2. Description of the Related Art
FIG. 1 is a systematic view illustrating a construction of a conventional air conditioner.
Referring to FIG. 1, the conventional air conditioner includes a compressor 11 for compressing refrigerant, a condenser 12 for removing heat from compressed refrigerant and dissipating removed heat to the outside, an expander 13 for expanding liquid refrigerant of a high pressure, and an evaporator 14 for evaporating expanded refrigerant to absorb heat so that a room temperature can be lowered. The refrigerant that passes through the evaporator 14, is fed back into the compressor 11 to complete the cycle. Since the condenser 12 and the evaporator 14 are equipped with fans thereby exposed to wind current, heat exchange can be smoothly executed.
The operation of the conventional air conditioner according to the aforementioned construction is described hereinafter. As mentioned above, when the refrigerant is compressed by the compressor 11, a vaporous refrigerant of the high temperature and pressure is discharged from the compressor 11. The liquid refrigerant of a high pressure is discharged from the condenser 12 as the vaporous refrigerant of high temperature and pressure is deprived of heat in the condenser 12, and the liquid refrigerant, which has been passed through the condenser 12, is expanded by the expander 13 becoming the refrigerant of low temperature and pressure. In the evaporator 14, the heat is transferred to the refrigerant of the low temperature expanded by the expander 13, causing the temperature of the area surrounding the evaporator 14 to decrease. Thus, the function of the air conditioner has been fully performed. The refrigerant that consumed the heat while passing through the evaporator 14, is fed back into the compressor 11 to be compressed again.
On the other hand, the air conditioner as described above in which a constant-speed compressor is adopted as the compressor, a room temperature is lowered when the air conditioner is operated by power supplied thereto, and the heat is quickly absorbed and removed by the evaporator 14 and the condenser 12, respectively. When the room temperature reaches the temperature set up in advance by a user and the room temperature is longer needs to be lowered, then the compressor 11, the evaporator 14 and the condenser 12 stop operating causing the room temperature to rise again.
FIG. 2 is a graph illustrating a room temperature change in a conventional air conditioner that adopts a constant-speed compressor. Referring to FIG. 2, an initial operation of the air conditioner rapidly drops the room temperature, and if the room temperature falls below the set temperature T1 and reaches the lower limit temperature T2 due to a rapid cooling occurrence, the operation of the air conditioner is interrupted (see section A).
Further, as the compressor 11 and the other parts of the air conditioner stop running at the lower limit temperature T2, the operation of the air conditioner is interrupted. Although the inside heat is not discharged to the outside, the room temperature rises as the heat is transferred to the inside of the room from the outside. Thereafter, when the room temperature rises beyond the set temperature T1 and reaches the upper limit temperature T3, the compressor 11 starts to operate again (see section B). As the room temperature reaches the upper limit temperature T3 and the compressor 11 and the other parts of the air conditioner begins operate again, the room temperature drops. Thereafter, as a room temperature drops below the set temperature T1 and reaches the lower limit temperature T2 again, the compressor 11 is deactivated, and heat discharge to the outside is suspended (see section C).
In the above descriptions, other than the initial operation period, the section A, the section B process in which the compressor 11 and other parts are deactivated causing a room temperature rises and the section C process in which the compressor 11 and the other parts are in an operation mode to make a room temperature to drop, are repeated. In this way, a room temperature is adequately adjusted. Hence, even if the air conditioner is in the operation mode, from the set temperature T1 the room temperature continues to shift between the upper limit temperature T3 and the lower limit temperature to maintain the room temperature.
This phenomenon where a room temperature fluctuates within a predetermined range between T2 and T3 while the air conditioner is operated, is called a hunting phenomenon. This hunting phenomenon results the room temperature to be unstably maintained, causing an inconvenience to the user of the air conditioner.
Although it may be possible to reduce the range between the lower limit temperature T2 and the Upper limit temperature T3 to minimize the temperature changes sensed by the user, frequent deactuations of the compressor 11 is resulted. Moreover, these frequent deactuations of the compressor 11 result in a problem in terms of efficiency since a great amount of energy is required for initial actuating of the compressor 11. Thus, reducing the hunting phenomenon may result in increase of the power consumption.
To cope with the aforementioned problem, a method for reducing the hunting phenomenon to ensure delightfulness and comfortableness of the user while reducing power consumption has been introduced. In this method, instead of the constant-speed compressor, a variable-speed compressor which is equipped with an inverter circuit, is adopted. By this, a compressing capability of a compressor can be changed depending upon a heat discharging load, in a manner such that the compressor is not frequently deactuated.
FIG. 3 is a chart for explaining an actuation of a conventional variable-speed compressor which is equipped with an inverter circuit.
Referring to FIG. 3, after an air conditioner is initially operated, if a difference between a set temperature which is set in advance by a user and a room temperature is no less than 2.5xc2x0 C., heat must be quickly discharged to the outside, and, to this end, the variable-speed compressor is actuated at a frequency of H6 which is a highest frequency under which the variable-speed compressor can be actuated. If the difference is between 2.0 and 2.49xc2x0 C., the variable-speed compressor is actuated at a frequency of H5 which is lower, by one step, than H6. Consequently, as a difference between the set temperature and a room temperature is gradually decreased, an actuating frequency of the variable-speed compressor is decreased. That is, if a difference is between 0 and 0.49xc2x0 C., the variable-speed compressor is actuated at a frequency of H1 which is a lowest frequency under which the variable-speed compressor can be actuated. Hence, the air conditioner is operated while an actuating frequency of the variable-speed compressor is changed depending upon a cooling load.
In the air conditioner to which the variable-speed compressor is applied, since a temperature is gradually and smoothly changed, the hunting phenomenon does not occur, and power consumption due to repetitive on/off switching of the compressor can be avoided.
However, the air conditioner, having applied thereto the variable-speed compressor, has a drawback in that, since the air conditioner includes the inverter circuit and the variable-speed compressor so as to be speed-variably controlled in its operation, a manufacturing cost is increased. Due to this drawback, the air conditioner having the variable-speed compressor is hardly used unless an air conditioner having a high compressing capability is required for precise temperature control.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a method for controlling an air conditioner having a multi-compressor in which air conditioner a plurality of compressors are used in place of costly equipment such as a variable-speed compressor, for compressing refrigerant, whereby an actuation of the multi-compressor is properly controlled in a manner such that the air conditioner can be operated in a more effective way.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for controlling an air conditioner having a multi-compressor, comprising the steps of: first determining, in order to accomplish a set temperature after a user starts the air conditioner, a cooling load of a room by measuring an on-time for which at least two compressors are run, in a manner such that the more the on-time of the compressors is long, the more the cooling load of the room is judged to be large; and operating the air conditioner by changing a compressing capacity of the compressors in response to a first determined cooing load, in a manner such that, when the cooling load is large, the air conditioner is operated by a first combination of compressors, having a large compressing capacity, and, when the cooling load is small, the air conditioner is operated by a second combination of compressors, having a small compressing capacity.
By the feature of the present invention, the method for controlling an air conditioner having a multi-compressor provides advantages in that, since respective compressors having different compressing capacities are properly selected and actuated, reduction in power consumption and proper control of a room temperature can be simultaneously attained.